The present invention provides a complex which is produced by reductive bacteria during the culturing process and consists of a culture medium component and a metal-reduction product, and also provides uses thereof. The complex according to the present invention is produced by reductive bacteria during the culturing process, and consists of a culture medium component and a metal-reduction product. The complex is an adsorbent for quickly and efficiently adsorbing ionic substances present in a solution, and also functions as a reducer for reducing prescribed noble metal ions and/or platinum-group metal ions